JERUSALEM- Israel on Sunday walked back part of its policy for third coronavirus vaccination shots, saying that contrary to a recent announcement, oncology patients should actually stick with two jabs only.

On Monday Israel began administering a third shot of the Pfizer/BioNTech inoculation to patients with compromised immune systems, including people who have had heart, lung and kidney transplants and some cancer patients.

But on Sunday, the health ministry said that after reviewing data on hundreds of patients from oncology wards, "the recommendation at this stage is to not vaccinate" cancer patients.

"Nearly 90 percent of the patients receiving chemotherapy developed antibodies following the (two doses of) vaccination, and the level of antibodies remained high a number of months after the vaccination," it said in a "clarification" to the health funds and hospitals administering the shots.

"In addition, the vaccination could have side effects... that could affect the oncological treatment," the ministry said.

Pfizer and BioNTech have said they would ask US and European authorities for permission to provide a third dose of their vaccine, but European regulators say it was too early to tell if a third was necessary.

The World Health Organization has expressed concern that such a booster shot could come at the expense of countries whose citizens have not yet received their first two doses.

Israel's initial vaccine rollout of the Pfizer/BioNTech jab was among the world's fastest, and helped to bring confirmed daily cases down to single digits last month.

It decided to go ahead with third shots in the light of evidence "that patients with immunosuppression do not develop an adequate antibody response after two doses" and after the number of daily cases began to rise.

A spokesman for Sheba medical centre, Israel's largest hospital, told AFP that "dozens" of cancer patients have received a third shot since Monday.